I really love this. Subject matter, palette, design, all of it. Subsequently, I'm blinded to any real points worth critting art wise. Compositionally speaking though, specifically, regarding the addition of Beelzebub, I'd say don't do it, personally. Despite the fact that the title is a line spoken by him, I don't think his inclusion is necessarry, or contextually relevant. Far as I remember this line comes before Lucifer is 'fully fallen' (and he still retains some of his former glory, his beauty), and you've depicted him here as the later, uglier Satan.
Dunno, I am probably just rambling, but I'd say, at the very least, you already have a pretty solid composition going on here. I would take the title as a title, and not bother with the lord of the flies, unless, of course, you just want to pixel him for the hell of it, in which case I say go for it. If your only reasoning is that 'he says it', though... yeah.
